moon fases

is the part towards the earth lightened up by the sun?

Just as the earth only half part of the moon is lightened up by the sun. It depends on the relative position of sun, moon and earth if the part towards the earth is lightened up by the sun. We speak of moonfases:

new maan = the moon is unvisible since the part towards the earth isn't lightened up

first quarter = the right half of the part towards the earth is lightened up

full moon = the part towards the earth is fully lightened up

last quarter = the left half of the part towards the earth is lightened up